At least in Wa, the term is "internal combustion engine" So technicaly glow is a no no. That being said, it's usually the noise that people object to. There is so little oil and such from our planes that it's rarely and issue. I live on a small electric lake, I ocasionally fly glow, but only in the midle of the day, and then usually 4stroke, which is much quieter than 2stroke. There were some kids running the glow proboat hydros, loud, buzzing other boats, not being courtious. They were eventually asked to leave and have not been back.

When deciding what is resonable, I try to think about what would bug me if I was trying to take a nap, enjoy the sun, relax, etc.

One thing to consider, electric has really come down in price, I recently converted a seamaster to brushless, and it can now be done for under $200, batteries included. No dead engines in the middle of the lake, very quiet. Take a look at United hobbies in china, it's slow, but cheap.